In the diagnosis and treatment of various diseases as well as in preventative health care, it is important to monitor the concentrations of certain ions (for example cations) in a patient's body. One cation which has merited considerble attention in the treatment of patients suffering from manic-depressive psychosis is lithium ion. Ohter instances where monitoring the concentration of this ion is important is in the treatment of alcoholics.
One type of electrode useful for determining the concentration of various ions, such as lithium, potassium, sodium, calcium and other cations in a fluid is generally composed of a reference electrode of some type and an ion-selective membrane. The reference electrode is a half-cell which contributes to providing a detectable potential during an assay. The ion-selective membrane can be made of glass or a polymeric binder material and is impregnated with an ion-sensitive carrier and a solvent for the carrier. The ion-sensitive carrier, also known as an ionophore, is a compound which is capable of sequentially complexing the desired ion, and transporting it across the membrane interface.
A significant advance in the art is the dry-operative electrode described in U.S. Pat. No. 4,214,968 (issued July 29, 1980 to Battaglia et al). The electrodes described therein have the advantage of providing reproducible potentiometric determinations of ion activity with no requirement for wet storage or preconditioning prior to use. This patent describes the electrodes as having a dried electrolyte layer comprising a solid salt dispersed in a hydrophilic binder. This electrolyte layer is also known in the art as a reference layer. Lithium ion-selective electrodes are described having cyclic polyethers as the ion carriers (Col. 16, lines 14-17).
Crown ethers have also been used as lithium ion carriers in lithium ion-selective membranes, as described for example by Kitazawa et al, Analyst, 110, pp. 295-299 (1985), and Kimura et al, J. Chem. Soc. Chem. Commun., pp. 669-700 (1985).
Phenanthrolines are known to complex and form coordination compounds with various cations, including alkali metal ions, alkaline earth metal ions and copper to name a few. For example, Pfeiffer et al (Zeitschrift fur anorganische und allgemeine Chemie, 239, pp. 133-144, 1938) describe the preparation of lithium complexes with a perchlorate of o-phenanthroline. Also, an abstract of U.S.S.R. Pat. 1,124,214 (published Nov. 15, 1984) describes a magnesium ion-selective membrane composition comprising a complex of magnesium and a phenanthroline modified with a tetraphenyl borate (as the membrane active compound) and a carrier solvent. The magnesium-phenanthroline complex appears to be the matrix for the ion-selective borate compound. An abstract of U.S.S.R. 989,441 (published Jan. 15, 1983) describes the use of bis(2,9-dimethyl-1,10-phenanthroline)cupripicrate in a copper(I) ion-selective membrane and electrode.
U.S. Pat. No. 3,483,112 (issued Dec. 9, 1969 to Ross) describes an anion-selective electrode sensitive to perchlorate, halide, nitrate and other anions. The selectivity is allegedly obtained using an ion exchanger liquid comprising a salt of the anion and a metal (such as copper, iron or cobalt) complexed with an oleophilic group-substituted phenanthroline.
Lithium ion-selective compositions and electrodes are described by Sugihara et al (Chem. Letters, 12, pp. 2391-2392, Dec., 1987) wherein 2,9-dimethyl- and 2,9-di-n-butyl-1,10-phenanthrolines are used as ionophores. Research in this area continues to provide highly accurate assays for lithium ion which can be used in clinical environments with high confidence.